1. Field of the Invention
The present invention relates to an adsorption bed and adsorption filtering system for removing airborne contaminants from clean rooms, sick buildings, or other enclosed spaces.
2. Related Art
Gas adsorption beds are used in many industries to remove airborne contaminants, such as organic bases, to protect people, the environment and often, a critical manufacturing process or the products that are manufactured. A specific example of an application for gas adsorption beds is the semiconductor industry where products are manufactured in an ultra-clean environment, commonly known in the industry as a "clean room". The manufacturing processes typically require the use of substances such as solvents to be used in the clean room environment. The use of these substances presents a problem because vapors that are present or are a byproduct from the process may contaminate the air and other processes in the room, such as lithography processes using chemically amplified photoresists, if not properly removed. In addition, environments may have several gases occurring naturally in the ambient air that contaminants that cannot be removed by particulate filters.
Typical contaminants are airborne bases, such as ammonia, organic amines, and N-Methyl-2-Pyrrolidone. To eliminate the problem, contaminated air is often drawn through a granular adsorption bed assembly having a frame and an adsorption medium, such as activated carbon, retained within the frame. The adsorption medium adsorbs or chemically reacts with the gaseous contaminants from the air flow and allows clean air to be returned to the process and/or the clean room. The removal efficiency is critical in order to protect the processes and the products. The removal efficiency and capacity of the gaseous adsorption bed is dependent upon a number of factors, such as the air velocity through the adsorption bed, the depth of the bed, the type and amount of the adsorption medium being used and the activity level and rate of the adsorption medium. It is also important that for efficiency to be increased or maximized, the air leaking through voids between the tightly packed adsorption bed granules and the frame should be eliminated.
Moreover, it is also important to have balanced flow distribution should more than one bed be used in parallel, so that all the beds can be changed at substantially the same interval while achieving a long life span for each bed. If flow is not distributed evenly, certain beds must be replaced before they are fully spent in order to maintain an acceptable safety factor. Moreover, it is important to accurately predict the adsorption activity of a bed that is typical of the deterioration rate of the active adsorption medium in the adsorption beds.
An example of such an adsorption bed and system is shown in U.S. Pat. No. 5,290,245, to Osendorf et al., and assigned to Donaldson Company, Inc., the Assignee of the present invention. Although the Osendorf patent shows beds which overcome the problems stated above, further improvements are possible.
It can be appreciated that if a measuring system could be utilized that uses a deterioration rate comparable to the adsorption beds, it can be reliably predicted when the beds will be spent. It can be appreciated that to maximize efficiency, even flow distribution should be accomplished with minimal pressure drop. The flow path along edges of adsorption medium in the beds should be longer to compensate for voids at the edges. Moreover, the footprint and space required for the adsorption beds and related flow distribution should be minimized. Such a system should provide a modular configuration for stacking of beds vertically and horizontally with easy removal and insertion and reliable sealing.